C++...

[Arpit]

trying a simple program...open a file, read and display the information in it...the program runs, and doesn't give me any errors whatsoever, but doesn't display the proper result either...what could be wrong??

#include "stdafx.h"

#include

#include

#include

#include

#include

int main()

{

ifstream Database("db.txt", ios::nocreate);

int ArtistNum = 0;

if (Database.fail())

{

cout << "File could not be opened";

return 0;

}

else

{

String TempArtist;

while (getline(Database, TempArtist))

{

cout << TempArtist << endl;

ArtistNum++;

}

return 0;

}

}

[Arpit]

it works if i change the string to char....but that's not what i really want...any other suggestions?

[h71y6]

Try using Cstring instead.

[azcodemonkey]

This worked for me. I don't know what string library you're using, but I used just and it worked fine.

<pre>

#include <iostream>

#include <stdio>

#include <fstream>

#include <string>



//---------------------------------------------------------------------------

using namespace std;



int main()

{

  ifstream DB("db.txt");

  if(!DB){

   cout << "File couldn't be opened" << endl;

  }

  else

  {

    cout << "File opened!" << endl;

    string dbtxt;

    while(!DB.eof())

    {

      getline(DB, dbtxt);

      cout << dbtxt << endl;

    }

  }

  return 0;

}

</pre>

[xWeston]

just use char arrays :)

[Arpit]

oh...maybe it was the wrong library :o

...i don't want to use char arrays because i need a jagged array and i don't know how to do that in C++

thanks for the reply!

[neowin_hipster]

the iostream library is only compatible with char arrays and the data type and is not meant to work with others, however, since the other string has the same name is still compiles. It should not compile though.

[Arpit]

here's what i'm trying to do...

i want to get the program to load artist names (one artist per line) into an array, so it's like

Input file..

U2

Celine Dion

Weezer

...

...

Array....

ArtistArray[0] = U2

ArtistArray[1] = Celine Dion

AritstArray[2] = Weezer

...

...

Now, since C++ doesn't have string arrays, I'm guesing that I'd have to use a 2D character array...in which 1st element would be the counter, and the 2nd element would be an array of characters for the name of the artist..

How do I go about doing that??...

Just to let you guys know...this is NOT for any school related thing, just a simple little application that I'm making (TRYING to make) myself to organize my mp3s a bit more...

[neowin_hipster]

You can do this. This is best option!!!

#include

#include

vector artists;

artists.resize(size) //change size at any time. Number of artists.

artist[1]="Celine Dion"

or you can do:

char artists[number_of_artists][50]; //names can be up to 50 long

cout<

artist[1][2]='g'; //set the 3rd letter of the 2nd artist.

[freestyle]

If you don't mind the stigma of using MFC, it has a CStringArray, and a CStdioFile which could prove usefull.

<pre>

CStdioFile fileMp3;

if (fileMp3.Open(_T("db.txt"), CFile::modeRead) == TRUE)

{

	CStringArray sArtistList;

	CString sLine;



	while(fileMp3.ReadString(sLine) == TRUE)

  sArtistList.Add(sLine);



	fileMp3.Close();

}

</pre>

[Arpit]

Sweet...thanks Goalie_CA!

...another thing...we use seekp and seekg to go to a desired character...can we do the same with lines instead of characters??

...if so, how?

[neowin_hipster]

Nope, unless you write your own function, very easy. I think I can write one. Ask me if you want it. But Here is a list of what you can do.

http://www.cplusplus.com/ref/iostream/fstream/

[azcodemonkey]

Using Goalie's suggestion to use a vector, you could also write it like so.

<pre>

#include <iostream>

#include <stdio>

#include <fstream>

#include <string>

#include <vector>

//---------------------------------------------------------------------------

using namespace std;



int main()

{

  vector<string> artists;

  ifstream DB("db.txt");

  if(!DB){

   cout << "File couldn't be opened" << endl;

  }

  else

  {

    cout << "File opened!" << endl;

    string dbtxt;

    while(!DB.eof())

    {

      getline(DB, dbtxt);

      artists.push_back(dbtxt);

      artists.resize(artists.size()+1);

    }

    for(unsigned int i=0; i < artists.size(); ++i)

      cout << artists[i] << endl;



  }

  return 0;

}

</pre>

If you're already doing that, way to go! :) If you want a sorted vector, just use the sort function in like so...

<pre>

  sort(artists.begin(), artists.end());

</pre>

For storing line position, use fstream::pos_type pos= DB.tellg(); while doing your getline. Then use DB.seekp(pos) to get the stored line position. I hope that is what you meant.

[Arpit]

thanks again!...

weenur, that was what i was doing myself :)

another question...

i'm trying to open another file, in which i want to begin reading line from the 39th character of the 6th line and onwards...so at every line, i begin reading from the 39th character.

if (!SongList)

cout << "File could not be opened";

else

{

int i = 0;

while (!SongList.eof())

{

while (i!=5)

{

getline(SongList, Temp);

cout << Temp << endl;

i++;

if (i==5)

break;

}

SongList.seekg(39);

getline(SongList, Temp);

cout << Temp << endl;

}

}

in this code...i managed to get to the 6th line without any problem, but when i did: getline(SongList, Temp); again (after the nested while loop)...it outputs the second line again...what should I do??

[neowin_hipster]

void GotoLineNumber(int LineNumber){

SongList.seekg(0);

for(int n=1;n

SongList.ignore(400,'n'); //ignores until 400 char or 'n' is read

};

}

GotoLineNumber(6); //goes to line 6.

SongList.seekg( SongList.tellg() + 39);

or try this:

SongList.seekg(39,ios::cur); goes to 39 with respect to current position.

SongList.getline(temp);

[Arpit]

Thanks again!

Another question...

I want to make a character array of the first element in my string array

For example...

ArtistArray[0] = {"Weezer"}

CharArtist[] = {'W','e','e','z','e','r','n'}

I tried to create a character array using vectors..

vector CharArtist = ArtistArray[0];

that gave me the following error:

error C2440: 'initializing' : cannot convert from 'std::string' to 'std::vector<_Ty,_Ax>'

with

[

_Ty=char,

_Ax=std::allocator

]

----------------------------------------------------------------------------

Then I tried to create using normal character array

char CharArtist[] = ArtistArray[0];

that gave me the following error

error C2440: 'initializing' : cannot convert from 'std::string' to 'char []'

...........what should I do??

[Arpit]

Wait...nevermind, I think I got it..

[neowin_hipster]

Never make a vector out of chars, use a string instead.

This will turn the string into a usuable format where only char array strings can be used.

Name.c_str()

Note: It adds a null to end of string. Even if there are null before before the end, it copies everything after too.

eg:

#include

#include //old c io. must use char array

int main(){

string hello = "Hello World";

printf(%s",hello.c_str()); //turn hello into char array.

return 0;

}

Output is "Hello" but string returned is "Hello World"

[Arpit]

This works as well...is it okay??

char ArtistName[] = "";

for (unsigned int b = 0; b < 1; b++)

{

// for (unsigned int c = 0; c < 1; c++)

for (unsigned int c = 0; c < ArtistArray.length(); c++)

{

ArtistName[c] = ArtistArray[c];

cout << ArtistName[c];

}

cout << endl;

}

[neowin_hipster]

Just do this:

<pre>

for (int n=0;n<number_of_artist;n++){

cout<<string[n]<<endl;

}</pre>

If you need the string in a char array format, use ArtistArray[n].c_str();

cout<

Why unsigned. It does same thing as int when accessing elements in an array, it just takes longer to type.

cout<

cout<

[Arpit]

this way i can use ArtistArray[n] directly as a character array as opposed to making a new character array and assigning the ArtistArray[n] values to that???

still a little confused how it works...working on it..

[Arpit]

...and then, how do i access each individual characters in that array??

[Arpit]

i seem to be able to access the characters individually if i do:

ArtistArray[0][0]

without having to do .c_str()....

Therefore, do I need to use .c_str() at all??

[neowin_hipster]

You can access characters individually.

<pre>

vector<string> hello(2);

hello[1]="Hello";

cout<<hello[1][0]; 

</pre>

OUTPUT:

H

c_str() is primarily used when you need the string in a char array format. Many functions don't accept string data type as a valid argument. Like printf. It only accepts char.

ex: printf("%s",string.c_str());

If you want to access single characters you shouldn't need to use c_str(). You can use [][]

Let's see your source and I can try and figure out what you are doing. I'm confused why you need it at all.

[Arpit]

alright...pretty long way now :)

...another question, quite unrelated to the previous ones...

i have a string array which contains the name of the mp3 files.

SongArray[0] = u2-stuck_in_a_moment.mp3

and i have a string array which contains the name of the artists

ArtistArray[0] = U2

now what i want to do is change the SongArray string so the artist name is omitted...and all "_", "-", ".", ".mp3"....omitted, then i want the remaining string in a new string array, so kinda like:

NameArray[0] = stuck

NameArray[1] = in

NameArray[2] = a

NameArray[3] = moment

the idea is to make the array shown above...doesn't matter how it's created. the ommitting stuff was just an option that i came up with which i thought might work, but not really sure how to go about it. if there's a better way, i'm all for it. :)

[Oogle]

Use strtok()

MSDN strtok() usage